So the state should be used to enforce your piety? On the list of crimes happening this hardly even ranks.
My piety? How's yours?
I would state that dancing on the ambo and ridiculing Orthodox gestures is an insult that was unecessary and didn't further any cause. To ridicule God in His own house is not acceptable to me. Perhaps you see it differently, and find what they did is permissable. That's just a reflection of your piousness.

Would you have felt differently if they had actually entered the Altar? Or would that be okay, as well, because they were trying to make a good point against government corruption?
As for comparing this particular act to other crimes...that's a poor argument...and this OP is strictly in reference to the Pussy Riot, and their efforts for publicity.
Feel free to start another thread on crimes of the MP, and I will be happy to join in, and support your views.
However, I cannot condone this act against Orthodoxy, MP jurisdiction, or not.
Seven years is too harsh, but, if these girls felt they had a right to demonstrate like this in a church, then the rest of us have a right to state that what they did was wrong.
I still say they should get some sort of community service...and perhaps a class in Orthodoxy.
They could have just as easily performed their stunt outside the church...but, no...they CHOSE to do it within the walls of a church.
Of course, there's always the option of turning the other cheek and letting God deal with them one day...